Mold and core construction



Oct. 19, i965 F. DERROR MOLD AND CORE CONSTRUCTION Filed July 1, 1965 3Sheets-Sheet 1 I6 II y y I? z Z \L x fivzyfi 22/ 7 \22 \24 INVENTOR Fl 2FRED L. DERROR ATTORNEYS Oct. 19, 1965 F. DERROR 3,212,156

MOLD AND CORE CONSTRUCTION Filed July 1, 1963 3 Sheets-Sheet 2 IO f 3INVENTOR. FRED L. DERROR ATTORNEYS Oct. 19, 1965 F. DERROR 3,212,156

MO LD AND CORE CONSTRUCTION Filed July 1, 1965 5 Sheets-Sheet 3 jINVENTOR.

////// FREDLDERROR ATTORNEYS United States Patent 3,212,156 MOLD ANDCORE CONSTRUCTION Fred L. Derror, Lucas, Ohio, assignor to MansfieldSanitary, Inc., Perrysville, Ohio, a corporation of Ohio Filed July 1,1963, Ser- No. 291,671 6 Claims. (Cl. 129) The present invention relatesgenerally to molds and cores. More particularly, the present inventionrelates to molds and cores for slip casting hollow ceramic shapes.Specifically, the present invention relates to molds and cores for slipcasting hollow ceramic shapes with coreformed passages therethrough andwithout air entrainment or internal tensile fractures.

The use of a mold and an interfitting core for slip casting hollowceramic shapes is well known to the art. However, considerabledifficulty has always been experienced when it was required to providethe cast item with through passages. For example, toilet tanks have beenslip cast for years and these items require passages through the bottomfor the water flow pipe as well as for the bolts which secure the tankto the member on which it is carried. Heretofiore, it has been theaccepted practice to cast the tank between a mold and core to providethe desired wall thickness. After the slip has cast up, the core isremoved, leaving the cast,i.e., initially set and partially cured, tankwithin the mold. A workman then inserts a template into the casting andusing this as a guide, takes various sized cutting punches and removesthose portions of the casings through which passageways are desired.This, however, is a tedious and time consuming task which has occasionedmany attempts to mold the passages directly into the casting.

Primarily'these attempts have utilized a resilient subcore attachedbeneath the primary core. A resilient subcore was thought to be thesolution since it is well known that the tolerances in the dimensions ofthe mold and core would not permit a sub-core to seat against the moldat the same time the primary core seated therein. It'was reasoned that aflexible sub-core would expand radially when seating against the bottomof the mold and then correspondingly contract to facilitate withdrawal.However, resilient materials are inherently wettable and slip, as itcasts, will adhere to a wettable surface. Therefore, when the sub-corecontracted upon withdrawal, the casting adhered to the sub-core andwould tear, or fracture, around the passage. I The lack of closedimensional tolerance between the mold and the core, which suggestedflexible sub-cores, also creates'another cause of damage to the castingswhich frequently relegates them to the scrap pile.

.When the liquid slip is poured into the mold a flash of the slip willform at the parting line between the top of the mold and that portion ofthe core which does not exactly seat on the mold. After the cast, and asthe moisture is further withdrawn from the slip, there is a large amountof shrinkage present. During the course of this shrinkage cracks oftenappear in the casting in the proximity to the flash. I have discoveredthat green cured casting material has relatively high shear strength butcomparatively low tensile and bending strength, and that thisundesirable cracking was occasioned because of these differentialstrengths, as will be hereinatfer more fully described. Furthermore,when the slip is poured into the cavity between the mold and theinterfitted core through funnels, as is the standard prior art practice,the slip flowing through the funnel creates a vortex which entrains airinto the slip. This air does not have the opportunity to escape beforethe slip casts and thus deleterious air bubbles are caused in the finalceramic item.

3,212,156 Patented Oct. 19, 1965 It is therefore an object of thepresent invention to provide an improved mold and core for slip castinghollow ceramic shapes with cored passageways therethrough.

It is another object of the present invention to provide an improvedmold and core, as above, having sub-cores for producing passages in saidcasting without tearing or cracking the casting upon withdrawal of thecore.

It is another object of the present invention to provide an improvedmold and core having sub-cores for producing passages through thecastings which will be effective irrespective of the dimensionalvariations existent in standard molds and cores.

It is another object of the present invention to provide an improvedmold and core which eliminates cracks in the casting in proximity to theflash by preventing the high shear strength of the green casting fromacting deleteriously upon itself.

It is a further object of the present invention to provide an improvedmold and core wherein the flash formation is oriented such that thestresses between the flash and the green casting act as bending forcesrather than shear forces.

It is a still further object of the present invention to provide animproved mold and core, as above, which eliminates the entrainment ofair into the slip as it is being poured into the cavity between the moldand the core to provide a deaerated casting. These and other objects ofthe invention, as well as the advantages thereof over existing and priorart forms, will be apparent in view of the following detailed tie--scription and the attached drawings and are accomplished by meanshereinafter described and claimed.

One preferred embodiment is shown by way of example in the accompanyingdrawings and hereinafter described in detail without attempting to showall the various forms and modifications in which the invention might beembodied; the invention being measured by the appended claims and not bythe details of the specification.

' In the drawings: FIG. 1 is a top plan of a mold and core according tothe present invention;

FIG. 2 is a cross section taken substantially on line 22 of FIG. 1;

FIG. 3 is an enlarged fragmentary area of FIG. 2 showing the greencasting with the flash attached thereto;

FIG. 4 is a view similar to FIG. 3 with the core removed;

FIG. 5 is a view similar to FIG. 4 depicting the casting after asutficient amount of the moisture has been removed to cause the castingto shrink and showing the flashing having been severed therefrom by theshrinkage;

FIG. 6 is a view similar to FIG. 3 depicting the prior art construction;

FIG. 7 is an enlarged cross section taken substantially on line 7-7 ofFIG. 2;

FIG. 8 is a view similar to FIG. 7 depicting the casting removed fromthe mold and core; and,

' FIG. 9 is a view similar to FIG. 8 showing the finished casting.

In general, a mold and core according to the present invention comprisesa hollow mold for receiving an interfitting core so as to form a cavitytherebetween in the shape of the article to be cast. A seat is providedon the rim of the hollowed mold for abutting a similar seat on thesupport shoulder of the core when the core is received within the mold.The abutting seats are angularly inclined, preferably at 49 fromhorizontal, in order to reduce the shear stress between the flash andthe main portion of the casting to an optimum amount and sub stitute abending stress therebetween.

A series of one or more sub-cores depend from the primary score to formthe necessary passageways through the casting. These sub-cores are ofsuch dimension that they do not ordinarily contact the mold but aredesigned to be preferably spaced apart from the mold approximately 4,

The cap portion of the core is provided with two wells, each of whichcommunicates with the cavity formed between the mold and theinterfitting core. One of the wells functions as a filling well with anoffset exit porch to reduce vortex and the other well acts as ashrinkage well. Both wells may be similarly constructed so that eithermay be the fill or shrinkage well.

Referring more particularly to the drawings, the mold, indicatedgenerally by the numeral 10, is hollow to receive the primary portion 11of the core, indicated generally by the numeral 12. The primary portion11 of the core 12 and the mold into which the primary portion 11 fits,form a cavity 13 therebetween in the shape of the article to be cast, atoilet tank being disclosed, although the concept of the presentinvention is readily adaptable to many other cast shapes.

The core 12 also has a cap portion 14 which extends transversely of theprimary portion 11 and forms a support shoulder 15 which rests againstthe upper edge of the vertical mold walls 16 to position the primaryportion 11 of the core 12 properly within the mold 10.

A seat 18 is formed on the undersurface shoulder 15 around the peripheryof the primary portion 11. The seat 18 engages a similar seat 19 formedon the upper edge of the mold walls 16. The abuttingly engaged seats 18and 19 are both inclined with respect to a horizontal reference for aparticular purpose.

The particular inclination, preferably 49", with respect to horizontal,obviates the undesirable cracking or fracturing of cast shapes whichoften occur in proximity to the flash on the upper edge of the castshape.

As shown in FIG. 6, the prior art mold had a substantially horizontalseat 19A on the top edge of the mold wall 16A which was engaged by asimilar substantially horizontal seat 18A on the shoulder 15A of thecore 12A. At places around the periphery of the mold the liquid slipenters into the crack between the seats 18A and 19A. This slip castswith the article, forming a flash 20A. As the article loses moisture itbegins to shrink. A portion of this shrinkage decreases the verticaldimension of wall 21A causing the top thereof to move vertically in thedirection indicated by the line marked with the letter X. The flash 20A,however, is prevented from moving downwardly with the wall 20A by thefixed position of 19A. These opposing vertical forces react as a shearstress along the vertical plane Y marking the jointer of the flash 20Awith the casting wall 21A. At the same time the downward force actsinternally of the wall 21A as a tensile stress.

I have found that the shear strength of green slip cast ceramic materialis far in excess of the tensile strength. Accordingly, the wall 21Aoften cracks or separates, as a result of the internal tensile stressalong a line such as marked with the letter Z in FIG. 6 before the shearstress was suflicient to separate the flash 20A from the wall 21A alongthe vertical plane Y.

A mold and core according to the present concept obviates thisdifficulty. As shown in FIG. 3, the slip will also invade any cracksbetween the seats 18 and 19 of the subject mold and core to form a flash20 as the slip casts. At this point it should be understood that moldsand cores alike are made from a water absorbing material such as plasterof Paris and it would not be practically or economically feasible tomachine fit the seats 18 and 19.

As depicted in FIG. 4, the core may be removed after the slip has cast.Here too, as the moisture is withdrawn, the wall 21 will shrink, aportion of this shrinkage tending to cause the top of the wall 21 tomove vertically downwardly in the direction indicated by the arrow X.The flash 20 is pl'eve lwd from moving with this vertical shrinkage ofwall 21 by the fixed position of seat 19.

The angular inclination of seat 19 provides both vertical and horizontalreaction forces against the slip 20, the resultant of which actsperpendicularly to the plane of seat 19, creating a bending moment aboutthe point Y. The extremely low bending strength of green cured, slipcast ceramic material causes the flash 20 to break away from the wall 21through point Y, as shown in FIG. 5, well prior to the time that thevertical components of the force acting on the flash 20 createsexcessive shear between the flash and the casting wall 21 or theinternal forces of the wall 21 exceed the tensile strength thereof. Thusthe cracking and fracturing of the wall of the casting has beeneliminated. It has been found that when seat 19 is inclined at an angleof approximately 49 from horizontal the most satisfactory results areobtained. See FIG. 5.

Referring again to FIG. 2, one or more sub-cores 22 are dependinglysupported from the underside of the primary portion 11 of the core 12.These sub-cores 22 are preferably of the same material as the primaryportion of the core and may be integrally formed therewith.

As has been previously discussed, it is impractical to machine set seats18 and 19. Accordingly, it is impossible to gauge the vertical dimensionof the sub-cores 22 such that their unde-rsurface 23 engages the bottomsurface 24 of the mold cavity just as the seats 18 and 19 engage.

For this reason, the prior art attempted to manufacture the sub-cores 22of an expansible material so that when the sub-cores contacted the moldbefore the seats 18 and 19 engaged, the sub-core would yield by lateralexpansion until the seats 18 and 19 were engaged. It was furthertheorized that such cores would contract when the core 11 was removedafter the slip had cast, supposedly facilitating removal of thesub-cores. However, the wettable, expansible materials provide surfacesto which the slip adheres as it casts so that the green casting wouldcrack in the vicinity of the subcores as the core was removed.

The present concept obviates this difficulty. The subcores 22 have thesame characteristics as the primary portion 11 of the core. That is,they are moisture absorbent and not wettable so the cast ceramicmaterial will not adhere to them, and the sub-cores 22 are constructedso that their vertical dimension brings them no closer to the bottomsurface 24 of the mold cavity than approximately & By this construction,the Sub-core never engages the mold before the seats 18 and 19 areengaged. Furthermore, the surface tension of the slip is such that itwill not flow into a crack of A or less. On the other hand, when thevariation of the mold dimension tends to the large size the spacingbetween the undersurface 23 of sub-cores 22 and the bottom surface 24 ofthe mold exceeds only a small flash 25 will be formed around theperiphery of the passageway 26 through the casting 27, as shown in FIGS.7 and 8, and this can easily be removed by the workmans finger or othersuitable tool when the green casting is removed from the mold, in orderto assure a satisfactorily uniform passageway 26, as shown in FIG. 9.

Finally, two slip wells 30 and 31 are provided in the upper surface 32of the cap portion 14 of the core 12. As best shown in FIGS. 1 and 2,each well 30 and 31 is substantially oblong in shape with a taperedfloor 33 intersecting a horizontal flow channel 34 at the base of eachwell. A vertical port 35 is positioned laterally adjacent one end of theflow channel 34 in a recess 36 in cap portion 14 which is laterallyadjacent to and communicates with, the well. Port 35 provides flowcommunication between the base of the well and the cavity formed betweenthe mold 10 and the interfitted core 12. The relatively horizontal flowchannel 34 and the laterally offset vertical port 35 assures that theslip can flow laterally into the port 35 in order to prevent theformation of a vortex as the slip leaves the well and flows into thecavity.

The elimination of vortical flow when filling the mold is especiallynecessary in slip casting ceramic material because of the undesirableair entrainment incident to vortical flow. Entrainment of air in theslip is especially undesirable since the cast, or initial setting, ofthe slip material will often occur before the air bubbles can risethrough the slip and exhaust. Larger air bubbles can cause destructivefaults in the casting, and particularly lower the internal tensilestrength to induce cracking along line Z. Smaller bubbles create what isknown as pin points or minute craters, in the finished glaze. Thepresent construction obviates the entrainment of air during the moldfilling process by the elimination of vortical flow into the moldcavity.

A mold and core constructed according to the concept of the presentinvention readily and economically produces a slip cast ceramic shapewith core formed passageways therethrough without the cracks which occurin proximity to the flash and without entrainment of destructive airpockets within the casing.

Accordingly, such a mold and core accomplish the objects of theinvention.

What is claimed is:

1. Mold and core construction of water absorbing material for slipcasting hollow, deaerated, ceramic shapes with at least one passagewaytherethorugh comprising, a hollow mold having a bottom surface and sidewalls terminating at an upper edge, a seat on the upper edge of saidwalls, a core having a primary portion and a cap portion, said primaryportion inserted within said mold to form a cavity between the mold andsaid primary portion, said cap portion forming a shoulder extendinglaterally of said primary portion, a seat on the under side of saidshoulder, said seats being inclined with respect to horizontal, at leastone sub-core carried on the primary portion of said core, said sub-corbeing also formed of a water absorbing material and extending to withinapproximately of an inch to the bottom surface of said mold, at leastone slip well in said cap portion adapted to receive slip from anexternal source, a horizontally oriented flow channel at the bottom ofsaid well, a port communicating between said well and said cavity, saidport communicating with said well at one end of and laterally offsetfrom said flow channel to prevent air entraining vortical flow betweensaid well and said cavity.

2. Mold and core construction of Water absorbing material for slipcasting hollow, deaerated, ceramic shapes with at least one passagewaytherethrough comprising, a hollow mold having generally vertical sidewalls and a bottom surface, said side walls terminating at an upperedge, a seat on the upper edge of said side walls, a core having aprimary portion and a cap portion, said primary portion inserted withinsaid mold to form a cavity between the mold and said primary portion,said cap portion forming a shoulder extending laterally of said primaryportion, a seat on the under side of said shoulder, said seats beingsubstantially engaged when said core primary portion is inserted withinsaid mold, said seats being inclined at approximately 49 fromhorizontal, at least one sub-core dependingly mounted from the primaryportion of said core, said sub-core being also formed of a waterabsorbing material and extending to within approximately of an inch ofthe bottom surface of said mold, at least one slip well in said capportion adapted to receive slip from an external source, a horizontiallyoriented flow channel at the bottom of said well, a recess in said capportion, said recess located laterally of and in communication with saidslip well, a port in said recess laterally of said flow channel, saidport communicating between said recess and said cavity.

Mold and core construction of water absorbent material for slip castinghollow ceramic shapes with at least one passageway therethroughcomprising, a hollow mold having side walls and a bottom surface, a corehaving a primary portion and a cap portion, said primary portioninserted within said hollow mold to form a cavity between said mold andcore primary portion, at least one sub-core carried on the primaryportion of said core, said sub-core being also formed of a waterabsorbing material and extending to within approximately of an inch ofthe bottom surface of said mold.

4. Mold and core construction of water absorbing material for slipcasting hollow, deaerated, ceramic shapes comprising, a hollow mold, acore having a vertically oriented primary portion and a cap portion,said core primary portion inserted within said mold to form a cavitybetween said mold and core primary portion, at least one slip well insaid cap portion adapted to receive slip from an external source, saidslip well being elongate along at least one horizontal axis, a recess insaid cap portion, a port communicating between said recess and saidcavity, said recess being positioned laterally of the elongate axis ofsaid well and communicating with said well to prevent air entrainingvortical flow between said well and said cavity.

5. Mold and core construction of water absorbing material for slipcasting hollow, deaerated, ceramic shapes comprising, a hollow mold, acore having a vertically oriented primary portion and a cap portion,said core primary portion inserted within said mold to form a cavitybetween said mold and core primary portion, at least one slip well insaid cap portion adapted to receive slip from an external source, ahorizontally oriented flow channel at the bottom of said well, a port atone end of and laterally offset from said flow channel, said portcommunicating between said Well and said cavity.

6. Mold and core construction of water absorbing material for slipcasting hollow ceramic shapes with at least one passageway therethroughcomprising, a hollow mold having a bottom surface and side wallsterminating at an upper edge, a first flash removing seat on the upperedge of said mold walls, a core having a primary portion and a capportion, said cap portion forming a shoulder extending laterally of saidprimary portion, said shoulder resting upon the upper edge of said moldto support said core therein, a second flash removing seat on the underside of said shoulder adjacent said core primary portion, said coreprimary portion vertically and removably inserted within said hollowmold to form a mold cavity therebetween, said first and second flashremoving seats being opposed when said core is inserted in said mold toallow formation of a flash therebetween, said first and second seatsbeing inclined at approximately 49 from horizontal, said inclinationsubjecting the flash to a bending stress as the ceramic shape greencures within said mold, and at least one sub-core dependingly mountedfrom beneath the primary portion of said core, said sub-core being alsoformed of a water absorbing material and extending to withinapproximately of the bottom surface of said mold.

References Cited by the Examiner UNITED STATES PATENTS 1,375,950 4/21Bewley 25-29 1,852,332 4/32 Perry 2529 1,921,240 8/ 33 Porter 22-2092,311,358 2/43 Baily 25130 2,683,298 7/54- Fadden 25-128 2,838,816 6/58Strom 22-134 3,136,024 6/64 La Monica 25-124 FOREIGN PATENTS 3,544 8/06Great Britain.

WILLIAM J. STEPHENSON, Primary Examiner.

MICHAEL V. BRINDISI, Examiner.

1. MOLD AND CORE CONSTRUCTION OF WATER ABSORBING MATERIAL FOR SLIPCASTING HOLLOW, DEAERATED, CERAMIC SHAPES WITH AT LEAST ONE PASSAGEWAYTHERETHROUGH COMPRISING, A HOLLOW MOLD HAVING A BOTTOM SURFACE AND SIDEWALLS TERMINATING AT AN UPPER EDGE, A SEAT ON THE UPPER EDGE OF SAIDWALLS, A CORE HAVING A PRIMARY PORTION AND A CAP PORTION, SAID PRIMARYPORTION INSERTED WITHIN SAID MOLD TO FORM A CAVITY BETWEEN THE MOLD ANDSAID PRIMARY PORTION, SAID CAP PORTION FORMING A SHOULDER EXTENDINGLATERALLY OF SAID PRIMARY PORTION, A SEAT ON THE UNDER SIDE OF SAIDSHOULDER, SAID SEATS BEING INCLINED WITH RESPECT TO HORIZONTAL, AT LEASTONE SUB-CORE CARRIED ON THE PRIMARY PORTION OF SAID CORE, SAID SUB-COREBEING ALSO FORMED OF A WATER ABSORBING MATERIAL AND EXTENDING TO WITHINAPPROXIMATELY 1/32 OF AN INCH TO THE BOTTOMSURFACE OF SAID MOLD, ATLEAST ONE SLIP WELL IN SAID CAP PORTION ADAPTED TO RECEIVE SLIP FROM ANEXTERNAL SOURCE, A HORIZONTALLY ORIENTED FLOW CHANNEL AT THE BOTTOM OFSAID WELL, A PORT COMMUNICATING BETWEEN SAID WELL AND SAID CAVITY, SAIDPORT COMMUNICATING WITH SAID WELL AT ONE END OF AND LATERALLY OFFSETFROM SAID FLOW CHANNEL TO PREVENT AIR ENTRAINING VORTICAL FLOW BETWEENSAID WELL AND SAID CAVITY.